In recent years, CAN-FD protocol, which has been developed based on CAN (trademark) protocol, is used widely. CAN-FD is a controller area network with flexible data rate. In CAN-FD protocol, a frame, which is transmitted and received, is provided with an arbitration area used for bus arbitration and a non-arbitration area for data storage. In the non-arbitration area, data transmission is made faster than in the arbitration area.
For suppressing waveform distortion in the non-arbitration area, in which high speed communications is performed, US 2014/0330996 (patent document) proposes to operate a driver so that a differential voltage having a polarity opposite to that of a dominant, is developed in a communications network at time of outputting a recessive. Since an error frame in the non-arbitration area cannot be detected in this case, it is proposed to detect the error frame based on a voltage level of the communications network.
However, in the conventional CAN, an output impedance of a transceiver is not normalized, that is, not regulated. In the conventional system proposed in the patent document, therefore, different potentials are generated at collision in correspondence to characteristics of transceivers connected to the communications network. It is thus impossible to detect the error frame stably.